1. Field of the Invention
The present invention relates to a semiconductor device and a semiconductor display device. Particularly, the present invention relates to a semiconductor device in which a nonvolatile memory for storing data and other logic circuits are integrally formed on an insulating substrate by using an SOI (Silicon On Insulator) technique. Moreover, the present invention relates to a semiconductor display device in which pixels and peripheral circuits such as a driving circuit and a memory are integrally formed on an insulating substrate by using the SOI technique.
2. Description of the Related Art
In recent years, a technique for manufacturing a semiconductor device, such as a thin film transistor (hereinafter referred to as a TFT), in which a semiconductor thin film is formed on an inexpensive glass substrate has been rapidly developed. The reason is that the demand for an active matrix type liquid crystal display panel (liquid crystal panel) has increased.
The active matrix type liquid crystal panel is constructed such that a TFT is disposed for each of several tens to several millions of pixel regions arranged in matrix, and an electric charge going in and out of each pixel electrode is controlled by the switching function of the TFT.
FIG. 14 shows a conventional active matrix type liquid crystal display device. As shown in FIG. 14, the conventional active matrix type liquid crystal display device includes a source line side driver 1401, a gate line side driver 1402, a plurality of pixel TFTs 1403 arranged in matrix, and a picture signal line 1404.
The source line side driver and the gate line side driver include a shift register, a buffer circuit, and the like, and are integrally formed on the same substrate as an active matrix circuit in recent years.
Thin film transistors using amorphous silicon formed on a glass substrate are disposed in the active matrix circuit.
There is also known a structure in which quartz is used for a substrate and a thin film transistor is formed of a polycrystalline silicon film. In this case, both a peripheral driving circuit and an active matrix circuit are constituted by thin film transistors formed on the quartz substrate.
There is also known a technique in which a thin film transistor using a crystalline silicon film is formed on a glass substrate by using a technique such as laser annealing. When this technique is used, an active matrix circuit and a peripheral driving circuit can be integrated on a glass substrate.
In the structure as shown in FIG. 14, a picture signal supplied to the picture signal line 1404 is selected by a signal from a shift register circuit of the source line side driver (shift register for horizontal scanning). Then the designated picture signal is supplied to the corresponding source signal line.
The picture signal supplied to the source signal line is selected by a thin film transistor of a pixel and is written into the designated pixel electrode.
The thin film transistor of the pixel is operated by a selection signal supplied from a shift register of the gate line side driver (shift register for vertical scanning) through a gate signal line.
This operation is sequentially repeated at suitable timing by signals from the shift register of the source line side driver and signals from the shift register of the gate line side driver, so that information is sequentially written into the respective pixels arranged in matrix.
In recent years, an active matrix type liquid crystal display device has been often used for a note-sized personal computer. In the personal computer, a multi-gradation liquid crystal display device is required to realize such functions that plural pieces of software are concurrently started up or a picture from a digital camera is taken in and is processed.
Moreover, the demand for a liquid crystal projector which can project a television signal such as a high-definition television signal and can meet a large screen, has increased. In this case as well, the quality of a supplied picture depends on the degree of the fineness of gradation display.
Like this, for the purpose of providing a high quality picture, it is important to what degree the gradation display can be made fine. As a method of gradation display, there are a case (analog gradation) of supplying an analog signal such as a video signal or a television signal to a source line and a case (digital gradation) of supplying a digital signal such as a data signal from a personal computer or the like.
In the analog gradation, as described above, an analog picture signal to be supplied to the picture signal line is sequentially selected by a signal from the source driver, and the designated picture signal is supplied to the corresponding source line.
In the digital gradation, a digital signal to be supplied to the picture signal line is sequentially selected, and after the selected signal is D/A converted, the designated picture signal is supplied to the corresponding source line.
In the case of the liquid crystal display device, even when any gradation display is used, there is a relation between the voltage (V) applied to a liquid crystal and the strength of transmitted light as indicated by a dotted line in FIG. 15. However, it is assumed that the liquid crystal display device uses a TN (twisted nematic) mode and a normally white mode in which the device becomes in a light state when a voltage is not applied.
As is understood from FIG. 15 as well, since there is a nonlinear relation between the voltage applied to the liquid crystal and the strength of the transmitted light, it is difficult to make gradation display according to an applied voltage.
In order to compensate the above, a means as gamma correction is adopted. In the gamma correction, a picture signal is gained and correction is made so that the strength of transmission light is linearly changed according to an applied voltage. By this gamma correction, excellent gradation display can be obtained. The relation between the applied voltage and the strength of the transmitted light in the case where the gamma correction is carried out is indicated by a solid line in FIG. 15.
However, in order to apply the gamma correction to a picture signal, an IC circuit is additionally required so that a circuit must be provided on the outside of the liquid crystal panel. Thus, it has been actually impossible to miniaturize a product.